This invention relates to hearing aids and more particularly to a method of fitting a hearing aid and to real-time hearing aid simulation.
Dispensing of hearing aids according to current practice is performed by audiologists or licensed hearing aid dispensers in accordance with a set procedure. First, an audiogram is recorded in a sound room by providing a pure tone to a patient at various frequencies, one at a time, at ever-decreasing amplitudes. The patient acknowledges the presence of the tone with a raised finger or hand. By employing this technique, the patient's hearing threshold is recorded across a frequency range of, for example, 125 Hz to 8000 Hz. In addition to the pure tone tests, a patient may be tested with speech stimulus to give an indication of what percentage of words the patient recognizes at a given signal level, or to determine the threshold of speech recognition. Once the hearing threshold and speech recognition threshold are determined, the audiologist reviews data describing the frequency response and amplification characteristics of various models of hearing aids, selects a particular hearing aid having characteristics which the audiologist determines would be most likely to provide improved hearing for the patient, and orders a unit of the selected hearing aid. The audiologist also takes an impression of the patient's ear and orders an ear mold of the proper shape and size to fit the patient's ear. The custom ordered hearing aid is fitted to the custom ordered ear mold, and is then ready for use by the patient.
In the United States, approximately 20% of all hearing aids that are dispensed by audiologists and hearing aid dispensers are returned because the patient is not satisfied. This might be because the patient's only involvement in the selection procedure is in the steps of determining the hearing and speech recognition thresholds.
It is known to employ a master hearing aid in fitting a patient with a target hearing aid. The master hearing aid is similar to a conventional hearing aid but includes a simple electronic filter that is intended to allow the master hearing aid to emulate a particular target hearing aid. However, such a master hearing aid only approximates the response of the target hearing aid since the actual response of the signal path that includes the target hearing aid is affected by a number of factors other than the frequency response of the hearing aid. For example, the hearing aid is held within the patient's ear by an ear mold, and the ear mold has vents that influence the acoustic signal that is generated in the patient's ear cavity.